Hydrogenases types

Iron Sulfur Compounds. Many molecular compounds (18—20) are known in which iron is tetrahedraHy coordinated by a combination of thiolate and sulfide donors. Of the 10 or more stmcturaHy characterized classes of Fe—S compounds, the four shown in Figure 1 are known to occur in proteins. The mononuclear iron site REPLACE occurs in the one-iron bacterial electron-transfer protein mbredoxin. The [2Fe—2S] (10) and [4Fe—4S] (12) cubane stmctures are found in the 2-, 4-, and 8-iron ferredoxins, which are also electron-transfer proteins. The [3Fe—4S] voided cubane stmcture (11) has been found in some ferredoxins and in the inactive form of aconitase, the enzyme which catalyzes the stereospecific hydration—rehydration of citrate to isocitrate in the Krebs cycle. In addition, enzymes are known that contain either other types of iron sulfur clusters or iron sulfur clusters that include other metals. Examples include nitrogenase, which reduces N2 to NH at a MoFe Sg homocitrate cluster carbon monoxide dehydrogenase, which assembles acetyl-coenzyme A (acetyl-CoA) at a FeNiS site and hydrogenases, which catalyze the reversible reduction of protons to hydrogen gas. 

The Mosshauer data performed on the as-isolated D. vulgaris [Fe] hydrogenase are in agreement with the EPR data, and further support the presence of two ferredoxin-type [4Fe-4S] clusters and that the H-cluster is in the diamagnetic state in the as-purified enzyme (169). 

Among several applications, Fe-based hydrogenases play a central role in the stepwise reduction of CO2 to methane. This process is accomplished through various types of Fe-hydrogenases however, in most of these enzymes, the active center is either a binuclear Fe-Fe- or an Ni-Fe-complex. Although the exact... 

The third type of hydrogenases from some methanogenic archea, also referred to as iron-sulfur-cluster-free hydrogenase, oxHmd, has attracted interest in bioinorganic... 

Other transformations supplied by these enzymes are para-ortho-hydrogen conversion, and the exchange reaction between H2 and protons of water.409-412 The hydrogenase enzymes found in various microorganisms are very different in their protein structure and in the types of electron carrier they use. 

Hydrogen production process by direct photolysis of hydrogen-containing compounds may be based on different types of photosensitizers in parallel with inorganic semiconductors. The model systems for photoinduced hydrogen production with porphyrins and hydrogenase were developed [4],... 

L. Florin, A. Tsokoglou, T. Happe (2001) A novel type of iron hydrogenase in the green alga Scenedesmus obliquus is linked to the photosynthetic electron transport chain. J. Biol. Chem., 276 6125-6132... 

There are several types of hydrogenases, all of which have a metal-containing active site. In fact, they are classified as Fe-only hydrogenases, Ni-Fe hydrogenases and Ni-Fe-Se hydrogenases. 

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